After a 2-1 win over Tampa Bay, Yankees manager Aaron Boone said Severino would travel with the club to Toronto for a weekend series against the Blue Jays.
Severino had been set to start Thursday night at Yankee Stadium against the Rays.
"He's just on the list now," Boone said when the initial roster move was announced. "Last night he got sick, had a fever and chills and all that. Doing a lot better today but we'll know [later]. I think his original rapid stuff was negative but we'll have a better idea probably sometime tonight."
Right-hander Clarke Schmidt started in place of Severino.
Severino is 4-1 with a 2.80 ERA and the 28-year-old right-hander was to have made his 100th career start in the series finale.
Schmidt, a 26-year-old right-hander, entered 3-2 with a 3.26 ERA in 11 relief appearances, striking out 15 and walking 10 in 19 1/3 innings.
New York selected the contract of right-hander Ryan Weber from Triple-A Scranton/Wilkes-Barre. Weber is 4-12 with a 5.28 ERA in seven major league seasons with Boston, Seattle, Atlanta, Tampa Bay and Milwaukee, and is 2-2 with a 2.95 ERA this year in four starts and four relief appearances in Triple-A.